one of these??
#1 check the battery voltage, after fully charging.
#2 ensure all cables are intact and fully connected,
#3 and ensure battery contacts are clean and make a good connection when the battery is slid home.
#4 check the crank axle for a magnetic disk and ensure its aligned correctly if fitted, these can easily get knocked out of place and cause issues..
your manual should list error codes , what does that say? google with the bike make and model with keywords 'manual pdf' if you no longer have a manual at hand if not already tried.